1. Field of the Invention
The present invention relates to an electron temperature measurement method, an electron temperature measurement program for implementing the method, and a storage medium storing the electron temperature measurement program.
2. Description of the Related Art
In recent years, as etching carried out on wafers (substrates) in a vacuum processing chamber (hereinafter merely referred to as the “chamber”) has been made finer and metallic films formed on such wafers in such a chamber have been made thinner, it has become required to precisely measure the state of plasma in the chamber, in particular plasma parameters.
A commonly known method of measuring such plasma parameters in such a chamber is a so-called Langmuir probe method in which a probe that has been given electrical potential is directly inserted into the chamber, and plasma parameters such as the plasma density, the electron temperature of the plasma, the plasma potential, and the sheath potential are measured based on the value of a current that flows through the probe due to collisions of electrons and ions in the plasma with the inserted probe.
In the Langmuir probe method, it is necessary to determine and then analyze the voltage-current characteristic, and hence the method is not suitable for reading the plasma parameters directly. A direct plasma parameter reading method in which the plasma parameters are read directly has thus been developed. In this method, two probes are used, the probes are set to suitably chosen potentials, and the plasma parameters are determined from the ratio of the currents flowing through the two probes simultaneously (see, for example, Japanese Laid-open Patent Publication (Kokai) No. H05-299194).
Furthermore, the frequencies of radio waves absorbed by a plasma change in accordance with the density of the plasma, and hence a plasma absorption probe method has also been developed in which radio waves of a plurality of frequencies are emitted from a probe inserted into the chamber, the extent of absorption of the radio waves at each frequency is measured, and the plasma density is estimated based on the measured extent of absorption of the radio waves.
However, none of the above methods have been adequate as a method of measuring the electron temperature as a plasma parameter.
For example, with the Langmuir probe method or the direct plasma parameter reading method, the measurement cannot follow rapid changes over time in the potential in the chamber caused by the application of radio frequency electrical power for producing the plasma, and hence the measured electron temperature is unstable and imprecise.
Moreover, with the plasma absorption probe method, only the plasma density can be measured; the electron temperature cannot be measured.